Role of autocrine Shh signaling in the potentiation of PDGF-BB–induced SMC migration and recruitment. PDGF-BB secreted by VEGF-stimulated ECs induces Shh expression in MCs. Locally, autocrine Shh promotes a sequence of events mediated by downstream signaling pathways via PI3Kγ and ERK1/2, leading to costimulation of PDGF-BB pathway targets. By this novel mechanism, Shh potentiates PDGF-BB–mediated NG2⁺ MC migration and recruitment on growing vessels allowing their long-lasting stabilization.